The present invention relates to an application and production of a magnetic product in environments where, for example it is desired to provide for or against the passage of electromagnetic radiation. Such applications may range from a shielding for a cable to a plastering for a wall of a room or rooms. While the present invention will be described with respect to the latter example, applications of the present invention is limited only by the imagination of one skilled in the art. The present invention relates particularly to magnetic material grain size. The related art sets out two examples of consideration of grain size in production and applications
Reference WO 92/08678 A1 concerns a magnetized product formed by the hardening of cement and water into a malleable mass. Such mass contains granular magnetic materials, including soft iron, thereby displaying certain magnetic properties. The material may be applied in electrical dynamos.
Reference EP 0393599 B1 sets out a surface mounted electrical coil which may be surrounded by a product of synthetic material wherein a powdery magnetic material such as carbonyl iron or ferrite is deposited.
Ferromagnetism refers to the physical phenomenon wherein certain electrically uncharged materials strongly attract others. Ferromagnetic materials, when exposed to magnetic fields, become easily magnetized and otherwise display strong magnetic properties. The magnetism in ferromagnetic materials is caused by the alignment patterns of the materials""constituent atoms, which act as elementary electromagnets. Ferromagnetic material may be considered as a comprising a large number of smaller regions, or domains, wherein the atomic or ionic magnetic moments are aligned. Where the combined moments of the domains are randomly oriented, the ferromagnetic material will not display any significant magnetic properties. However, when an external magnetic field is applied, the moments will rotate into alignment with the field, thereby reinforcing one another and causing magnetic properties of the material as a whole to be displayed. Such alignment continues until a point of saturation, particular to individual ferromagnetic materials. Examples of such materials includes, iron, cobalt, nickel, alloys or compounds containing each, along with some rare earth metals, as known to one skilled in the art.
Ferrite is a ceramic-like ferromagnetic material having a variety of applications. A determining factor of ferrite grain size, in a given material, is its initial permeability which refers to the initial slope of the magnetic flux density (B), established within the material by a magnetizing field, versus the magnetic field strength (H) of the magnetizing field. The slope is typically characteristic of an unmagnetized ferromagnetic material and otherwise represents the magnetic permeability under very small-applied magnetic fields. Magnetic permeability refers to the relative increase or decrease in the resultant magnetic field inside a particular material as compared with the magnetizing field wherein the material may be located. Magnetic permeability is typically assigned the Greek character mu and defined as B/H.
Returning to ferrite, a determination of essential grain size is the initial permeability. The initial permeability of a solid including ferrite therein depends on the ferrite grain size diameter and its relative size with respect to domains of the solid material. A typical domain has a diameter of about 0.5 microns. Where the average grain diameter size of ferrite approaches the size of the domain, initial permeability is reduced. The reduction occurs because the number of domains per grain dramatically drops, such that the alignment of the domains in response to an applied magnetic field discontinues.
It is therefore an object of the invention to set out an apparatus and method for making it of ferromagnetic material having an elevated or maximized initial permeability. In particular, the material is applicable to shielding for frequencies of above 100 kHz, and in particular 1 MHz to 2 GHz. It is another object of the invention to provide a method which can be implemented so as to enable mass production at reasonable engineering effort and expense and with maximally replicable component characteristics.
The present invention comprises a magnetic device comprising a plurality of ferromagnetic material grains, said grains having a minimum diameter larger than an average domain diameter of said grains, and said grains further embedded in a matrix. The present invention further comprises a method for producing a magnetic device, comprising the steps of: forming ferromagnetic grains, said grains having an average diameter greater than domains of said grains; and embedding said grains in a matrix, said matrix comprising a hardening material.